The present invention pertains to an apparatus and method providing substantially two-dimensionally uniform irradiation of large areas with a high level of radiation. More particularly, the present invention pertains to an apparatus for and a method of uniformly projecting a high level of radiation onto a large planar target surface so as to uniformly treat the surface.
Various manufacturing processes include treating a planar surface by irradiating the surface with, for example, ultraviolet light or other radiation. The radiation treatment may be related to curing, purification, disinfection, advanced oxidation or some other procedure. By way of example, manufacturing of printed circuit boards frequently involves forming conductive paths by a photoresist process in which a board treated with a photoresist in a desired pattern is irradiated as a part of a process to remove material from specified areas on the board. Similarly, in some printing processes a printed pattern is cured by irradiating the pattern. Obtaining a high quality, uniform product requires irradiating a two-dimensionally uniform high level of radiation over the entire target area. Otherwise irregularities in the finished product may result.
Existing devices often expose the central area of the irradiated surface to more radiation than the edge areas of the surface. The areas of high radiation may receive more than the desired level, possibly causing damage, while the areas of low radiation may be undertreated.
Various techniques have been used in the past to control the uniformity of irradiation of planar target surfaces. By way of example, U.S. Pat. No. 4,010,374 discloses an ultraviolet light processor including a primary light source which exposes a target surface on a work piece to ultraviolet light with the ultraviolet flux incident per unit area of the target surface greater at the central region of the surface than at edges of the surface, and a secondary light source which is positioned in a different plane than the primary light source and which exposes the target surface to ultraviolet light with the ultraviolet flux incident per unit area of the surface greater at the edge areas of the target surface than at the central region. Not only is such an ultraviolet light processor complex and expensive to manufacture and to operate, but also it is difficult to control in a manner that maintains the ultraviolet radiation received at the edge areas of the target surface from the secondary source at substantially the same level as the ultraviolet radiation received at the central area of the target surface from the primary source.
U.S. Pat. No. 4,276,479 discloses a tunnel type irradiation chamber with a plurality of cylindrical ultraviolet lenses through which an object to be treated is conveyed. Two sets of radiation sources, providing light of two different wavelengths, are within the chamber, providing light in two stages. Not only is this apparatus complex to control, but also it does not provide uniform radiation distribution on the object surface.
U.S. Pat. No. 4,348,015 shows a radiation projection system including complex lenses in order to provide uniform irradiance. Numerous other systems have been attempted. These generally are complex and expensive, both to construct and to operate. Even so, they generally have difficulty in achieving uniform irradiance, particularly two-dimensionally uniform irradiance.
The present invention is an apparatus for and a method of providing substantially two-dimensionally uniform irradiation of large areas with a high level of radiation. In accordance with the present invention at least two substantially identical sources of radiation are provided for producing radiation to irradiate a target surface. Each source may include an elongated discharge bulb. Each bulb is arranged within a corresponding elongated elliptical reflecting trough, with the bulb being spaced from the focal axis within the trough. The troughs, with the radiation sources in them, are positioned side by side in a plane substantially parallel to a planar target surface. Preferably, planar reflectors extend from the troughs to the target surface, being pivotally attached to the troughs so as to accommodate various sizes of target surfaces. Preferably also, planar reflectors extend from the interior longitudinal edges of the troughs, the inner reflectors being pivotally attached to the troughs to permit adjustment of the angular position of the inner reflectors so as to optimize the uniformity of the radiation distribution on the target surface. Each of the sources of radiation can be a light source, preferably a source of ultraviolet light such as a microwave electrodeless discharge bulb, an arc discharge bulb, or a fluorescent discharge bulb, for example.
In a preferred embodiment of the present invention, the positions of the troughs are adjustable in the direction of the minor axes of the ellipses defining the troughs, likewise aiding in optimization of the uniformity of the radiation distribution on the target surface.